Post Information

If you’re shopping for a wood pergola kit, you’ll be making decisions for your outdoor pergola about a variety of topics including wood type, pergola dimensions, design style, attached to a wall or freestanding, and about the size and installation of the posts that are the legs for your pergola. It is important that your pergola is level and well anchored in order to ensure proper installation and structural integrity.

Pergola Post Length

We offer posts with standard lengths of 8 feet, 10 feet and 12 feet. When trying to decide the length of pergola posts needed for your wood pergola kit, there are a few things to consider.

  1. Desired height above ground. The height to the bottom of the beam (low point of the roof structure) is 4 inches less than the length of the post, for example it would be 7 feet 6 inches for an 8 foot post or 9 feet 6 inches for a 10 foot post mounted at ground level;
  2. Post installation method, whether you are installing either buried in a concrete footer, or installed on top of a concrete footer or existing concrete slab; and
  3. If installing buried in a concrete footer, then you will need to add the length of the post below the ground to the desired height of the posts.

To determine the length below ground, we recommend at least 2 feet or more depending upon the frost line and building codes in your area. Do you live in a northern state where the ground is frozen for certain months out of the year, or a southern state where the ground does not freeze? If you live where the ground freezes you will want to be sure that you set your posts or footings deeper than the frost line. This will ensure that frost heave will not pop your pergola out of the ground like a cork. The correct depth can be determined by checking with your local building code department or online resource. In warmer climates you may be able to use 10′ posts, which would be buried 2′ in the ground, and colder climates will most likely use 12′ posts which would be buried 3-4′ in the ground.

Pergola Post Installation

Mounted on Concrete Footer or Existing Slab

The easiest method of installation is to dig footings to the correct depth (below the frost line in your area) and use post mounting hardware to attach the posts to the concrete footings or existing concrete slab as follows: Order the 8 foot or 10 foot post option and add the post attachment hardware to your order. This will connect the pergola posts to the footings or slab, and also hold the bottom of the post up 1″ from the concrete surface to keep the bottom of the posts out of water that may accumulate on the patio.

Here are pictures of the post bases that would be provided (6×6 and 4×4):

Make sure if you will be setting the posts on top of footings, that the footings are dug below the frostline (if there is a frost line in your area) as pictured here:

installing posts for pergola

Note: When you add your pergola kit to the cart, if you selected Post Will Be Going “On concrete slab or footer (10’ posts with mounting hardware)” or “On concrete slab or footer (8’ posts with mounting hardware)”, the hardware has already been added to your kit. If you made any other selection and you’d like to purchase mounting hardware, simply add that selection to your cart from the Accessories section. If you will be installing your pergola on a concrete patio or concrete footings choose Concrete Anchor. If you are installing on top of a wood deck (not recommended) choose Wood Lag.

In Ground (buried in concrete footer) Installation

If you will be sinking your posts into the ground (buried in a concrete footer) you have two different options on how to pour the concrete around the posts:

Option #1 – Works in warm climates where the ground does not freeze.

Option #2 – For climates where the ground freezes.

Notice option #2 has a flared bottom. When the concrete is set below the frost line and flared on the sides this prevents the frozen ground that will be pushing on the sides of the concrete from popping it out of the ground. Also the use of concrete form tubes helps this because the smooth surface of the tube will not allow the ground to grab the concrete and pull it up. We also recommend if you are putting the pergola posts in ground, that you wrap the bottom part of the post that will be in contact with cement in a peel and stick roofing membrane which can be purchased at your local hardware store.

If you follow these suggestions you are sure to have a pergola that will stay put where it was intended to be for the life span of the lumber. Take a shortcut and you’re bound to have a pergola that is out of level. Frost heave can push posts out of the ground 3″ or more if not installed properly.

concrete post for wood pergola

Option #1 – Works in warm climates where the ground does not freeze.

concrete post for wood pergola

Option #2 – For climates where the ground freezes.

Here’s a great video on how to pour concrete footings the correct way:

If you have any questions about pergola post depths and options, please contact us and we’ll be happy to help you. You can find more info and tips about pergolas on our FAQs and Tips.

Related topics: Pergola wood types, How to measure for a pergola, Pergolas for sale in custom sizes, Pergola footprint diagram.